Disruptive behavior disorders are characterized by antisocial, aggressive behaviors. Externalizing problems are the most commonly diagnosed mental health problems of childhood. They tend to be stable over time, resistant to treatment, and linked to psychiatric disorders in adolescence and adulthood. Early onset aggression is a precursor of life-course persistent antisocial behavior. Little is known, however, about constitutional and environmental factors, and their interactions, that contribute to different developmental outcomes. Eighty-two 4-5 year-old children at low, moderate or high risk for later disruptive behavior disorders (based on initial levels of externalizing problems), have been studied at three subsequent time points; 6-7, 8-10, and 12-13 years. Social, emotional, cognitive, and physiological areas of child functioning are examined, in conjunction with socialization experiences. The goal is to identify key factors that contribute to continuity and change over time in young children's behavioral problems. Several child and parent risk and protective factors that contribute to continuity versus amelioration of problems during middle childhood were previously reported. The findings from four new projects are summarized next. (1) Observed socialization processes contributed to patterns of continuity and change in disruptive problems over time. Maternal emotion played a crucial role in the development of stability and improvement of early externalizing problems even when the presence of preschool problems was controlled. In particular, mothers who showed less anger toward their disruptive children had children who showed lower levels of aggression as they grew older. (2) Children's representations of conflict and distress during symbolic play showed substantial continuity from 5 to 7 years of age. Boys showed more anger and forceful, dysregulated aggression, while girls showed more sadness, affiliation, reparation and comforting behaviors. These gender-based themes intensified with age, indicating processes implicated in differences in the types of emotional and behavioral problems that emerge in boys and girls over time. (3) Early cortisol reactivity, a physiological stress response, predicted mother and teacher reports of internalizing problems (anxiety, depression, somatic complaints) and externalizing problems (aggression, antisocial, disruptive behaviors), both concurrently and at two later time points. Attentional problems were predicted more consistently for boys, whereas depression, anxiety, and aggression were predicted more consistently for girls. (4) A subset of children without serious problems was compared with Japanese chldren in determining the role of culture in the socialization of young children's responses to frustrating situations. IN these normative samples, Japanese mothers focused more on achieving solutions to these problems in a harmonious, interdependent manner. In contrast, U.S. mothers emphasized the importance of independence and individuality in problem resolution.